1. Field of the Invention
Example embodiments generally relate to an assist mechanism for efficiently positioning a unit of an image forming apparatus such as a paper feed device or a duplex unit, and an image forming apparatus incorporating the assist mechanism.
2. Description of the Related Art
Image forming apparatuses, such as copiers, facsimile machines, printers, and multifunction devices having at least one of copying, printing, scanning, and facsimile functions, typically form a toner image on a recording medium (e.g., a transfer sheet) based on image data using electrophotography.
For example, an image forming device of the image forming apparatus forms a toner image on a transfer sheet conveyed from a feed device of the image forming apparatus including a paper tray storing a plurality of transfer sheets. Although the paper tray can be pushed into or pulled into or out of the feed device, if the paper tray is not properly positioned in the paper feed device, the image forming device forms a faulty image on the sheet, with the image deviating from the center of the sheet in a width direction of the sheet.
To prevent such improper positioning, some related-art image forming apparatuses include a positioning device including a pressing device and a stopper mechanism. The stopper mechanism controls movement of a paper tray, and includes a stopper and a blocking member. When the pressing device presses the paper tray to make the stopper contact the blocking member, the paper tray is properly positioned in a feed device, so that an image can be formed on the center of a sheet in a width direction of the sheet. In addition, the stopper mechanism controls movement of the paper tray, thereby preventing the paper tray from sudden removal from the feed device.
When the paper tray is empty, or when a user wants to change a sheet size or the like, the user pulls the paper tray out of the feed device by pulling a lever to release control of the stopper mechanism. After supplying a new sheet to the paper tray, the user pushes the paper tray into the feed device. However, when the paper tray is too heavy, in order to attach the paper tray to the feed device, the user has to press the paper tray with much force, causing deviation of a sheet from a proper installation position or damage to the paper tray.
Other related-art image forming apparatuses include an assist mechanism for automatically pulling a paper tray into a predetermined position of a feed device. Such automatic assist mechanism can reduce the burden on the user, as well as reduce the impact of the paper tray on the feed device during insertion of the tray, thereby preventing deviation of a sheet from a proper position or damage to the paper tray.
However, because the assist mechanism continues to pull the paper tray after attachment of the paper tray, when the pulling force is greater than the force with which the pressing device pressers the paper tray, the stopper does not contact the blocking member and the paper tray cannot be positioned properly at a predetermined position. However, when the pulling force is smaller than the pressing force of the pressing device, the paper tray supplied with sheets cannot be automatically pulled into the feed device. As a result, the user has to push the paper tray into the feed device unassisted.
Accordingly, there is a need for a technology capable of properly positioning the feed tray unit at a predetermined position in the feed device of the image forming apparatus.